The present invention relates to a safety valve for a timepiece, according to the introductory part of claim 1.
From CH 682 199 it is known to equip a timepiece with a safety valve in order to prevent in the inside of the timepiece an excess pressure with respect to the pressure of the surroundings, which forms under certain conditions.
An excess pressure in the inside of the timepiece may have the following origin:
If a timepiece, proceeding from a situation in which the inner pressure firstly corresponds to the outer pressure, is subjected to a higher pressure in the surroundings then it is possible for some matter to diffuse through the sealing means into the inside of the timepiece and thus cause an increase in pressure in the inside of the timepiece, or an adaptation of the pressure. If this timepiece is then subsequently subjected to a significantly lower pressure of the surroundings within a relatively short time, then the excess pressure in the timepiece existing with respect to the surroundings may for example lead to the fact that the timepiece glass bursts open and sensitive components of the timepiece are damaged.
Such changes in pressure may for example occur in the process of diving, be the timepiece in gaseous surroundings such as is the case with a diving bell, or directly located in the water. Amongst the substances which may diffuse through seals into the inside of the timepiece is above all to be mentioned the element helium with its very small atomic dimension. Helium not only penetrates into the timepiece when it is subjected to the helium atmosphere common to diving bells, but also dissolves out of the water at great depths, i.e. at a high pressure.
The safety valve shown in the above mentioned document CH 682 199 comprises two O-rings and a screwable cover for closing the valve. With an unscrewed lid only one of the two seals functions, whereas with a screwed down lid, both arranged behind one another ensure an improved sealing. The lid is screwed down before the diving procedure and the valve closed, so that on diving, with an increasing pressure of the surroundings, the entry of material with larger atomic dimensions such as water and dirt particles can be prevented. In order subsequently to effect a rapid reduction of the excess pressure forming with a jump-like part ascent, before the ascent the cover is to be unscrewed and the valve to be released so that helium may escape.
In the case that the lid is not screwed down before the diving procedure, small quantities of water and dirt particles may reach into the inside of a timepiece and the sealing properties of the safety valve may worsen.